Quasi 500-year Cycle Signals in Solar Activity

Abstract

Direct observations of solar activity are available for the past four century, so some proxies reflecting solar activity such as 14C, 10Be and geomagnetic variations are used to reconstruct solar activity in the past. In this present paper, the authors use rectified wavelet power transform and time-averaged wavelet power spectrum to investigate long-term fluctuations of the reconstructed solar activity series. The results show an obvious quasi 500-year cycle exists in the past solar activity. Three reconstructed solar activity series from 14C variations confirm the periodic signals.

1. Introduction

Solar activity has a profound influence upon geodynamics processes, and the Sun directly or indirectly affects some terrestrial phenomena on the Earth. Some studies showed variation of solar activity closely relates to global and regional climate change (Rasmus, 2006; Miyahara et al., 2008; Mendoza & Velasco, 2009; Ogurtsov et al., 2013; Dergachev et al., 2016). After analyzing the solar variation, global and regional sea-surface temperature, Weng (2005) concluded that inter-annual and centennial climate change signals were not purely internal, but also external because of the existence of the solar activity cycle. Kilcik et al. (2008) made use of surface air temperature, pressure and tropospheric absorbing aerosol data as climate parameters and solar flare index data as solar activity indicator, to study effect of solar activity on the surface air temperature of Turkey. With Indian temperature series of more than one-hundred years, Aslam (2014) investigated the influence of solar activity on regional climate. Results indicated that the solar variation may still be contributing to ongoing climate change.

The solar activity can influence atmospheric circulation on various time scales, and variations of the atmospheric circulation then impact precipitation process in some areas (Ratnam et al., 2014). Ma et al. (2007) investigated the connection between Indian summer monsoon rainfall and solar activity series, and believed that the solar variation affects the Indian rainfall variation to some extent. Taking into account reconstructed precipitation series in Huashan mountain area of China and solar variation series, the influence of solar activity on the Huashan mountain precipitation to some extent was found (Ma et al., 2010).

More and more people attach importance to studies about long-term solar variation (Usoskin & Mursula, 2003; Yin et al., 2007; Ma, 2007, 2009). However, direct observations of solar activity in the past four centuries are insufficient to calculate the long-term solar variation. Some proxies including 14C, 10Be and geomagnetic variations can reflect the solar activity. Therefore, solar activity in the past can be reconstructed with these proxies. In this work, rectified continuous wavelet transform reveals quasi ~500-year cycle signals existing in the reconstructed solar activity series. […]

4. Conclusion

In this work, the reconstructed sunspot number series in the past are analyzed to research for quasi ~500-year cycle signals. Results of the rectified wavelet analysis show the obvious time-variable characteristics exist in the solar variation. Periodic amplitude of this cycle changes with time and it is not a cycle in the strict periodic sense but rather cyclicity with a varying time scale. The quasi ~500-year cycle may be a periodic signal in the solar activity, and attention should be paid to it when the long-term fluctuation in the solar variation is studied.